In this population-based study of 15 600 children aged 3 to 6 years from Tianjin, China, children of higher weight percentiles at birth had a significantly increased risk of hypertension in both boys and girls. Moreover, children whose postnatal weight percentiles moved upward from birth to childhood had a significantly increased risk for hypertension. The associations of birth weight and postnatal weight change with childhood hypertension were not significantly modified by birth size for gestational age.
Previous studies on the association of birth weight and childhood hypertension were conducted largely in Western countries. Studies on birth weight in Chinese populations and other developing countries are sparse. Caution should be taken when generalizing findings from Western countries to other populations because of differences in genetic predisposition, the distribution of anthropomentrics, behaviors, and other factors that contribute to hypertension across populations. Findings from the present study do correspond with those of a study conducted within a US population.18
This study identified an increased risk for high systolic and diastolic blood pressure with increasing birth weights among participants in the US Collaborative Perinatal Project. In addition, children who traversed weight percentiles upward were at increased risk of high blood pressure in early childhood.18
However, in contrast, a majority of published studies reported an inverse association between birth weight and hypertension in childhood.19
Such inconsistency in findings may be attributed, at least in part, to differences in study population and analytical approaches across studies. Different from the majority of previous studies, we did not control for children's current weight in the analyses of the association between birth weight and hypertension because of the concern of over adjustment.
Current weight may mediate the association between birth weight and hypertension.20
In addition, the observed significant association may be attributed to a common cause of both birth weight and hypertension. For example, genetic factors may predispose an individual to a particular birth weight and hypertension.21
Adjustment for current weight may artificially attenuate or reverse the association between birth weight and hypertension. Nevertheless, our findings of a positive association between birth weight and risk for childhood hypertension were comparable to findings from the Collaborative Perinatal Project,18
adapting the similar analytical approach of not adjusting for current childhood weight.
Studies associating birth weight with childhood- and adult-onset diseases are motivated by the fetal origins or developmental programming hypotheses, which describe how exposures at critical periods of development can affect long-term developmental changes.22
Birth weight, as a proxy for the nutritional status of the intrauterine environment, in a majority of studies has been found to be inversely associated with hypertension as a result of impaired renal development.23
However, this association between low birth weight and future hypertension may only describe 1 tail of the distribution. Indeed, the association between birth weight and metabolic disorders may not be linear; rather, it may be described by a J- or U-shaped association.22
Studies have identified an increased risk for metabolic disorders at both ends of the birth-weight distribution, suggesting a role for early overnutrition in the development of hypertension.10,11
A U-shaped association also has been identified between birth weight and cardiovascular risk factors,24
type 2 diabetes,25
and all-cause mortality,26
such that both the lowest and the highest birth weights are associated with increased risk. This observation leads to the expansion of the developmental origins of health and disease theory to include the role of excessive fetal growth and early overnutrition. This may particularly be relevant in Chinese populations where the influx of the Western lifestyle is escalating, and, as a result, the occurrence of macrosomia, childhood obesity, hypertension, and other metabolic diseases are increasing rapidly.12
Moreover, in China, conventionally, greater birth weight is an indicator of healthy infants. Because of the 1-child policy, pregnant women are highly encouraged to consume more food and nutrients during pregnancy to ensure a healthy infant and an infant of higher birth weight, as evidenced by the very low prevalence of low birth weight in the present study.
The prevalence of low birth weight in this population was very low (~1%), which limited the statistical power to detect a significant association between low birth weight and hypertension. It is the higher end of the birth weight distribution that is captured to a greater degree in the present analyses. We did identify a moderate but nonsignificant increase in the risk for hypertension among male infants of low birth weight (<2500 g) compared with those with normal weight (2500–3000 g) (OR: 1.71 [95% CI: 0.94–3.11]).
These analyses were conducted in a large, representative cohort of children from Tianjin, China. Additional study strengths include the validity of measurements, including birth weights and lengths abstracted from birth certificates and accurate current hypertension and weight measurements, which were administered by intensively trained health workers. Analytical strengths include the assessment of confounding factors, such as socioeconomic factors and evaluation of the full range of potential association between birth weight and hypertension via splines and fractional polynomials.
There are several limitations. The childhood weight measurements were taken at a single time point. Although cross-sectional analyses evaluating weight gain from birth to different age points suggest that the age of weight gain is important, a longitudinal assessment would be necessary to determine whether cumulative weight gain versus weight gain at a specific age contribute to hypertension.